Module split: extract audio I/O helpers to server/audio.js

• getAudioDuration(path)         — ffprobe wrapper, returns seconds | null
  • splitAudioFile(in, dir, secs)  — ffmpeg -acodec copy chunking
  • downloadPodcastAudio(url, dst) — streams HTTP audio to disk

Also moved fetchUrl into util.js (alongside the other stateless
helpers) — it's a generic HTTP-GET-with-redirects used by RSS parsing
and channel discovery, not strictly audio.

server/index.js: 2758 → 2694 lines.

Smoke tested: server boots; /api/license-status, /api/health, /
respond. No behavior change.

server/util.js

@@ -1,6 +1,9 @@
-// Pure helpers — no module-scoped state, no Express, no I/O effects.
-// Anything in here is safe to import from any other module without
-// worrying about ordering or initialization side effects.
+// Stateless helpers — no module-scoped state, no Express, no
+// initialization side effects. Anything in here is safe to import from
+// any other module without worrying about ordering. A few helpers do
+// I/O (fetchUrl) but only when called.
+
+import https from "https";
 
 // ── SSE helper ──────────────────────────────────────────────────────────────
 // Writes a single Server-Sent Events frame: `event: X\ndata: Y\n\n`.
@@ -89,6 +92,27 @@ export function safeText(result) {
   return "";
 }
 
+// ── HTTP GET with redirect following ────────────────────────────────────────
+// Returns the response body as a string. Follows HTTP redirects up to a
+// reasonable depth (relies on https module's default behavior plus a one-
+// level recursion). Used for fetching RSS feeds, channel pages, etc.
+//
+// For binary downloads (e.g. podcast audio), use audio.downloadPodcastAudio
+// — it streams to disk instead of buffering in memory.
+export function fetchUrl(url) {
+  return new Promise((resolve, reject) => {
+    https.get(url, (res) => {
+      if (res.statusCode >= 300 && res.statusCode < 400 && res.headers.location) {
+        return fetchUrl(res.headers.location).then(resolve, reject);
+      }
+      let data = "";
+      res.on("data", (chunk) => (data += chunk));
+      res.on("end", () => resolve(data));
+      res.on("error", reject);
+    }).on("error", reject);
+  });
+}
+
 // ── Retry helper for transient Gemini API errors ────────────────────────────
 // Retries on 503/429 and on common transient network errors. Linear backoff
 // (delayMs * attempt). The optional `log` callback receives a one-line